There have been known various bush cutting machines which include a throttle adjustment unit mounted in a prime mover for adjusting the rotational speed of a cutter blade, and a brake unit provided in a drive power transmission path between the cutter blade and the prime mover for applying the brakes to the cutter blade. Typical examples of such bush cutting machines are disclosed in Japanese Utility Model Laid-Open Publication No. SHO-51-53248 and Japanese Patent Laid-Open Publication No. SHO-52-145135.
The bush cutting machine disclosed in SHO-51-53248 comprises a rotary cutter or blade connected to the prime mover via a clutch and a driven shaft, and a handle carrying a brake lever connected via a wire to a brake shoe of the brake unit. When the brake lever is released from a gripped state, the brake shoe is urged against an outer circumferential periphery of the driven shaft to apply the brakes to the rotary cutter.
In the thus-arranged bush cutting machine, for adjusting the rotational speed of the rotary cutter using the throttle lever, an operator is required to perform respective operations of the throttle lever and the brake lever in a well-timed fashion during a bush cutting operation, for example, by operating the throttle lever in such a manner as to gradually increase the rotational speed of the rotary cutter while gripping the brake lever to gradually release the brakes from the rotary cutter, thus requiring the operator to have a skill in operating the levers. Further, since the operator needs not only to perform a lever operation with his hand but also to maintain an attitude of the bush cutting machine during work, the levers must be desirably operated in a possible simplest way with a view to improve workability and minimize operator's fatigue.
The bush cutting machine disclosed in SHO-52-145135 comprises a cutter blade connected to the prime mover via a rotary shaft, a handle rod mounted to an operation rod through which the rotary shaft passes, a brake lever and a throttle lever both mounted to the handle rod, a brake lever connected via a wire to a brake section for braking the cutter blade, a throttle lever connected to a throttle valve mechanism via a wire, and a control box provided midway of the wires for linking the wires to one another. The control box includes a control body rotatably secured to a pivot shaft. The wires are connected to respective ends of the control body.
In the bush cutting machine of SHO-52-145135, the brake section and the throttle valve mechanism are interlinked to each other through operation of the brake lever. However, the presence of the control box provided midways of the wires makes the structure complicated with a resultant difficulty compelled in assemblage of the control box and the wires. Further, in the bush cutting machine, since an outer tube between the control box and the throttle lever and the outer tube between the control box and the throttle valve mechanism warp largely and return to their original positions upon operation of the throttle lever, the outer tubes interfere with an operator and disturb his work. Moreover, the control box has component parts, provided at the pivot shaft, the control body and the respective ends of the control body, for mounting the wires, thereby increasing the number of component parts.